Netherlands captain Mark van Bommel has claimed that Thursday's open training session was marred by racist chants aimed at Oranje's black players.
Around 25,000 people came to watch Bert van Marwijk's men in action as they prepare for Euro 2012, but it has been reported that a small contingent of those present directed their attention to members of the Dutch squad.
On the instructions of the AC Milan midfielder, the players moved their equipment and training drills to the other side of Wisla Krakow's stadium, and the incident left the veteran fuming.
"It is a real disgrace especially after getting back from Auschwitz [the Dutch squad had visited the concentration camp on Wednesday] that you are confronted with this," the 35-year-old told the waiting media after the session.
"We will take it up with Uefa and if it happens at a match we will talk to the referee and ask him to take us off the field."
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He added: "At least now we know what we can encounter. Very atmospheric."
Jetro Willems, Netherlands' youngest player in the squad has remained quiet on the subject, and told AD SportWereld: "Jungle noises? I haven't heard any."
Uefa has confirmed that the training session was interrupted by some protesters but denied that they had racist connotations. An official discussed the situation with the Dutch squad, and was told that the chanting had not been racially motivated, with the protests believed to be in response to Krakow not being used as a host city during the tournament.
But when pressed by members of the Dutch media into commenting on what had occurred, Van Bommel added: "You need to open your ears. If you did hear it, and don't want to hear it, that is even worse."
Uefa have a staunch zero-tolerance policy on racism within football and Euro 2012 has already been the subject of reports and documentaries about racist and anti-Semitic behaviour in both host nations, Poland and the Ukraine.
The host cities chosen by Europe's football governing body are Gdansk, Poznan, Wroclaw and capital city Warsaw.